I was finally able to register for this promo today, but have now completed most of my stays for the promo period
I also managed to register at last following this link.
http://www.hiltonhhonors.com/milesandmoreccen
This is how easy it is: book a qualifying stay at any of the participating Hilton hotels, between 25 May and 31 July 2010, and you can earn up to 5,000 award miles.
To take advantage of this offer, simply register at
http://www.hiltonhhonors.com/milesandmoreccen. You will receive 1,000 award miles for every qualifying stay.